A Deuteron Magnetic Resonance Study of Urea-d4

A deuteron magnetic resonance study has been made on a single crystal of urea-d4. At room temperature deuteron quadrupole coupling corresponding to a stationary molecule is obtained. The eqQ and η values determined are: eqQ⁄h=210.8±1.0 kc./sec. and η=0.139±0.010 for D1, and eqQ⁄h=210.7±1.0 kc./sec. and η=0.146±0.010 for D2 at room temperature, and eqQ⁄h=206.3±1.2 kc./sec., η=0.138±0.010 for D2 at 117°C. In both cases the maximum field gradient component and the N–H direction are in good agreement. The onset of reorientational motion about the C=O bond of a whole molecule has been concluded from the line-width change at high temperatures. Above 110°C the effect on the line-width of the reorientation about C–N bond has also been observed. The barrier heights for these motions are estimated to be 11±2 kcal./mol. for the reorientation about the C=O bond and 15±3 kcal./mol. for that about the C–N bond. The temperature dependence of the quadrupole splitting and that of the dipole coupling between 14N and D have been observed and dicussed in relation to the motion of the urea molecule.